Passive skills have had a long and storied history. When Diablo III debuted at the WWI 2008, skill trees included passive skills, much like in Diablo II. In 2010, it was announced that passive skills had been renamed traits and separated out from active skills. At the July 2011 Press Event, Blizzard announced that passive skills were once again in the game, replacing the traits system.
Berserker Rage was first revealed in the July 2011 Press Event with a listed level of 1 (presumably so players could try it out from the beginning).